Open the picture in your potograph, picture software. Look for a button, or a pull down menu with the word "RESIZE." Select this tool or function and type 640 into the width. Usually the height will self adjust to keep the proper ratio. Resave the picture. Sometimes you should rename it as well so then you will have two copies, one large high resolution the other smaller and low resolution. This is one way I'm certain there are other means. Best of luck and it certainly sounds as if it is the '77.